1. Field of the Invention
This invention relates generally to a power divider suitable for microwave bands, and more particularly to a distributed-line power divider having a filter function.
2. Description of the Related Art
A power divider and a filter are useful as circuit elements in a microwave circuit of a microwave transmitter, receiver or the like.
Currently, power dividers of the described type are known which comprise, as shown in FIG. 10 of the accompanying drawings, a pair of quarter-wavelength transformers 31, 32 disposed between a common port 1 and a pair of distributing ports 2, 3. In the power divider, the microwave power inputted from the common port 1 is equally divided by the distributing ports 2, 3, and reversely the microwave powers inputted in phase from both the distributing ports 2, 3 are composed and then outputted to the common port 1. This prior divider is disclosed in, for example, an article "A Class of Broadband Three-Port TEM-Mode Hybrid" (S. B. Cohn) in IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol. MTT-16, No. 2, February 1968, pages 110-116.
In the meantime, a known filter is exemplified by a low-pass filter such as shown in FIG. 11 which has open stubs 34 connected to a high-impedance line 33. This prior filter is disclosed in, for example, a book "Microwave Filters, Impedance-Matching Networks, and Coupling Structures" (G. L. Matthaei, L. Young and E. M. T. Jones) McGraw-Hill Book Company 1984.
In microwave circuits, it has currently been a common practice to use a filter as connected in series with a power divider. However, the filter and the power divider are separate circuit elements independent of each other and, therefore, the number of total parts to be used in the circuit is increased, which will result in a large-sized circuit. Particularly for realizing a microwave circuit in an IC form, the number of total parts must be reduced to minimize the area which is to be occupied by the circuit elements.
Furthermore, because quarter-wavelength transformers are used, the prior power divider is necessarily large in size. For example, in the case of FIG. 10, the length L2 between the end of the distributing common port 1 and the end of the distributing ports 2, 3 is about 60 mm.